Friction bush

ABSTRACT

A friction bush for imparting twist to a moving yarn is described wherein the bush overcomes the prior art problem of generated heat on the friction surface of elastomeric coated bushes. Generated heat buildup and corresponding degradation of the elastomeric surface is reduced by utilizing a highly conductive metal bush coated with a thin layer, i.e., less than about 2 millimeters of elastomeric material, as the friction surface, thereby providing rapid conduction of heat away from the frictional surface.

United States Patent [191 Doschko et a1.

FRICTION BUSH Inventors: Werner Doschko, Nussloch am Leimbach; Wolfgang Fohlisch, Nussloch; Alfred Wensch, Bad-Mingolsheim, all of Germany Imperial Chemical Industries Limited, London, England Filed: Mar. 2, 1973 Appl. No.: 337,336

Assignee:

Foreign Application Priority Data Mar. 7, 1972 Great Britain 10498/72 US. Cl. 57/77.4 Int. Cl. D02g 1/04 Field of Search 57/77.3-77.45,

References Cited UNITED STATES PATENTS 5/1960 Russell et a1 57/77.4

Primary Examiner-Donald E. Watkins Attorney, Agent, or Firm-Herbert M. Adrian, Jr.

[57] ABSTRACT A friction bush for imparting twist to a moving yarn is described wherein the bush overcomes the prior art problem of generated heat on the friction surface of elastomeric coated bushes. Generated heat buildup and corresponding degradation of the elastomeric surface is reduced by utilizing a highly conductive metal bush coated with a thin layer, i.e., less than about 2 millimeters of elastomeric material, as the friction surface, thereby providing rapid conduction of heat away from the frictional surface.

9 Claims, 4 Drawing Figures FRICTION BUSH The present invention relates to improved friction bushes for imparting twist to moving yarns.

It is well known to texturise yarns; particularly yarns of synthetic thermoplastic materials such as polyesters and polyamides; by twisting the yarn, setting the yarn in its twisted state and subsequently detwisting the set yarn, this process is known as false twisting. Various methods have been proposed for imparting a twist to the moving yarn and the present invention is concerned with devices which rotate and impart twist to the yarn by virtue of frictional contact between the device and the yarn.

It has been proposed that yarn may be twisted by passage through a rotating tube wherein the inner surface of the tube against which the yarn bears is a friction surface so that the rotation of the tube imparts a twist to the yarn. It has also been proposed to use a rotating cup, the inside and top surfaces of which provide friction surfaces against which the yarn is held by some form of yarn guide. This type of device has the advantage that the yarn approaches and leaves the device from the same side thus making threading up easier. In devices of these types the friction surface is generally provided by a thick rubber bush which is shaped to give the desired contact between the yarn and the bush. However, this creates two disadvantages, firstly the frictional contact between the yarn and the bush generates considerable heat and, as the bush is of thick rubher, this heat is not conducted away. Accordingly, the area where the yarn contacts the rubber becomes extremely hot during a long run which results in damage to both the yarn and the friction surface. Furthermore, the continual contact between the yarn and the friction surface tends to scratch and mar the friction bush which produces an uneven surface which can damage the yarn and necessitates renewal of the friction surface. In addition, as the friction bush wears, yarn of variable quality is obtained according to the part of the bush in contact with the yarn, thus yielding yarn of bad uniformity.

It is an object of the present invention to overcome these disadvantages.

According to the present invention we provide a friction bush for imparting twist to a moving yarn comprising a rotatable metal portion shaped to provide an area for contact with the yarn said metal portion being coated over at least that part of its surface which contacts the yarn with a layer of friction material no more than 2 millimetres thick, said friction material having a shore hardness at room temperature greater than 30.

The invention will be more readily described by reference to the drawings wherein:

FIG. 1 is a plan view ofa friction bush in accordance with the present invention;

FIG. 2 is a sectional view along the line 2 2 of FIG. 1 showing the cross-section of the bush;

FIG. 3 is a plan view of another friction bush in accordance with the present invention; and

FIG. 4 is a sectional view along line 4 4 of FIG. 3 showing the interior curvature portion of the bush.

Referring more particularly to the Figures, bush comprises a high heat conductive metal having coated thereover a thin layer of friction material l2.

The friction bush of the present invention may be such that the metal portion forms a bore through which the yarn passes and in this embodiment the metal should be shaped so that there is contact between the yarn and the friction surface as the yarn passes through the bore. Alternatively, the bush may be of a type where the yarn approaches and leaves the bush from the same side and is held against the friction surface by a suitable form of yarn guide system. In this embodiment the metal portion is cup shaped and coated with the friction material over the area of contact with the yarn, which may be the inside surface, the rim of the cup, or both.

The choice of metal is not critical although we prefer to use aluminium because with the high speeds of rotation that are used it is useful to have a light bush. Furthermore, aluminium has high heat transfer. The form in which the metal portion is shaped should preferably ensure adequate contact between the yarn and the bush without any dramatic changes in yarn direction while it is in contact with the friction surface because dramatic changes in direction tend to result in yarn breakages. Thus the preferred shape will depend on the yarn path for example if the bush is formed with a bore we prefer that the entrance to the bore is tapered so that it is wider at the point where the yarn enters. In this way if the yarn enters the bush at an angle to the axis of the bore it will run up the tapered portion and through the bore, giving effective contact with the friction surface without any dramatic change in yarn direction. Similarly we prefer that the exit end of the bore is also tapered to allow a smooth exit for the yarn.

The coating on the metal which provides the friction surface may be of any suitable material providing it has a sufficiently high coeeficient of friction to ensure that twist is imparted to the yarn and providing it has a shore hardness at normal temperatures of at least 30. We do, however, prefer that the material has a shore hardness of at least 50 and preferably between 50 and 90. Our preferred coating materials are the polyurethane rubbers having the properties specified above. In particular we prefer to use the Flexane polyurethanes rubbers as supplied by Devcon Limited.

It is necessary to ensure good adhesion between the friction surface and the metal and we find that if the friction surface is of a polyurethane rubber, satisfactory adhesion may be achieved by simply coating the polyurethane on the metal and leaving it to cure. Curing accelerators may be included in the polyurethane but this is not preferred as their presence tends to reduce the adhesion to the metal. We also prefer that the metal be treated to enhance the adhesion between the metal and the coating which provides the friction surface. Our preferred treatment comprises etching the metal surface preferably by means of a first coating of a primer. The choice of primer will of course depend upon the nature of the material forming the friction surface.

The friction bushes of the present invention may be used to produce twist in any yarns having a positive friction surface. The bush is rotated by any suitable means and the yarn is held against the friction surface so that the rotation of the bush imparts a twist to the yarn. the friction bushes of the present invention are particularly useful in false twist processes in which the yarn first passes through a heater and then to the false twist bush so that the twist imparted by the bush runs back along the yarn into the heater zone where the heat 3 sets the yarn in its twisted state. After passing through the friction bush the yarn is untwistedto provide a bulked yarn.

The device can be used to false twist. drawn sythetic thermoplastic yarns, synthetic yarns drawn immediately before texturising and undrawn synthetic yarns, e.g., yarns from nylon 6, nylon 6.6, polyester etc. As described above, false twisting is a process in which yarn is twisted so that the twist runs back along the yarn into a zone where it is heated and the twist set. In this technique the action of the twist bush is two-fold in that it imparts a twist' in the yarn that is being fed to the bush and detwists the yarn as it leaves the bush. The techniques of the present invention may readily be used in the twisting step of such a process;

The thin friction surface together with the metal backing has high heat conductivity and thus the heat generated by frictional contact between the yarn and the bush is dissipated. In this way yarn breakages and deterioration of the friction surfaces are reduced.

. We claim:

1.,A friction bush for imparting twist to a moving yarn comprising a rotatable rigid metal portion shaped to provide an area for contact with the yarn said metal portion being coated over at least that part of its surface which contacts the yarn with a layer of frictional material no more than 2 millimetres thick, said friction material having a shore hardness at room temperature greater than 30.

2. A friction bush according to claim 1 in which the metal portion is of aluminium.

3. A friction bush according to claim 1 in which the metal portion forms a bore through which the yarn passes.

4. A friction bush according to claim 1 in which the metal portion is cup shaped and the yarn approaches and leaves the bush from the same side thereof.

5. A friction bush according to claim 3 in which the bore of the bush is tapered so that it is wider at the point where the yarn enters the bore.

6. A friction bush according to claim 1 in which the friction material has a shore harness of at least 50.

7. A friction bush according to claim 6 in which the friction material has a shore harness of less than 90.

8. A friction bush according to claim 1 in which the friction material is a polyurethane rubber.

9. A friction bush according to claim 1 in which the metal portion is treated to enhance the adhesion between the metal and the friction material. 

1. A friction bush for imparting twist to a moving yarn comprising a rotatable rigid metal portion shaped to provide an area for contact with the yarn said metal portion being coated over at least that part of its surface which contacts the yarn with a layer of frictional material no more than 2 millimetres thick, said friction material having a shore hardness at room temperature greater than
 30. 1. A friction bush for imparting twist to a moving yarn comprising a rotatable rigid metal portion shaped to provide an area for contact with the yarn said metal portion being coated over at least that part of its surface which contacts the yarn with a layer of frictional material no more than 2 millimetres thick, said friction material having a shore hardness at room temperature greater than
 30. 2. A friction bush according to claim 1 in which the metal portion is of aluminium.
 3. A friction bush according to claim 1 in which the metal portion forms a bore through which the yarn passes.
 4. A friction bush according to claim 1 in which the metal portion is cup shaped and the yarn approaches and leaves the bush from the same side thereof.
 5. A friction bush according to claim 3 in which the bore of the bush is tapered so that it is wider at the point where the yarn enters the bore.
 6. A friction bush according to claim 1 in which the friction material has a shore harness of at least
 50. 7. A friction bush according to claim 6 in which the friction material has a shore harness of less than
 90. 8. A friction bush according to claim 1 in which the friction material is a polyurethane rubber. 